Modified Series Arc Welding And Improved Control of One Sided Series Arc Welding

ABSTRACT

An electric arc welding system for depositing weld metal along a groove between two edges of a metal workpiece where the system contains a first power supply and a second power supply, each providing a welding waveform to respective welding electrodes. The positive output terminals of both power supplies are coupled to the same contact tip and the negative output terminal of one of the power supplies is not coupled to the workpiece.

PRIORITY

The present application is a continuation-in-part of and claims priorityto U.S. patent application Ser. No. 11/327,736, filed Jan. 9, 2006, theentirety of which is fully incorporated herein by reference; and acontinuation-in-part of and claims priority to U.S. application Ser. No.11/465,999, filed Aug. 21, 2006; which is a continuation of U.S.application Ser. No. 10/754,836, filed Jan. 12, 2004, the entireties ofwhich are fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the art of electric arc welding andmore particularly to improved series arc welding and modified series arcwelding.

INCORPORATION BY REFERENCE

Embodiments of the present invention are directed to an electric arcwelding system utilizing high capacity alternating circuit power sourcesfor driving two or more tandem electrodes of the type used in seamwelding of large metal blanks. Although the invention can be used withany standard AC power supply with switches for changing the outputpolarity, exemplary embodiments use power supplies with the switchingconcept disclosed in Stava U.S. Pat. No. 6,111,216 wherein the powersupply is an inverter having two large output polarity switches with thearc current being reduced before the switches reverse the polarity. Thepower source can be a chopper operated at high switching speeds.Consequently, the term “switching point” is a complex procedure wherebythe power supply is first turned off awaiting a current less than apreselected value, such as 100 amperes. Upon reaching the 100 amperethreshold, the output switches of the power supply are reversed toreverse the polarity from the D.C. output link of the inverter. Thus,the “switching point” is an off output command, known as a “kill”command, to the power supply inverter followed by a switching command toreverse the output polarity. The kill output can be a drop to adecreased current level. This procedure is duplicated at each successivepolarity reversal so the AC power supply reverses polarity only at a lowcurrent. In this manner, snubbing circuits for the output polaritycontrolling switches are reduced in size or eliminated. Since thisswitching concept is preferred to define the switching points as used inthe present invention, Stava U.S. Pat. No. 6,111,216 is incorporated byreference as though fully set forth herein. The concept of an AC currentfor tandem electrodes is well known in the art. U.S. Pat. No. 6,207,929discloses a system whereby tandem electrodes are each powered by aseparate inverter type power supply. The frequency is varied to reducethe interference between alternating current in the adjacent tandemelectrodes. Indeed, this prior patent of assignee relates to singlepower sources for driving either a DC powered electrode followed by anAC electrode or two or more AC driven electrodes. In each instance, aseparate inverter type power supply is used for each electrode and, inthe alternating current high capacity power supplies, the switchingpoint concept of Stava U.S. Pat. No. 6,111,216 is employed. This systemfor separately driving each of the tandem electrodes by a separate highcapacity power supply is background information to the present inventionand is incorporated herein as such background. In a like manner, U.S.Pat. No. 6,291,798 discloses a further arc welding system wherein eachelectrode in a tandem welding operation is driven by two or moreindependent power supplies connected in parallel with a single electrodearc. The system involves a single set of switches having two or moreaccurately balanced power supplies forming the input to the polarityreversing switch network operated in accordance with Stava U.S. Pat. No.6,111,216. Each of the power supplies is driven by a single commandsignal and, therefore, shares the identical current value combined anddirected through the polarity reversing switches. This type systemrequires large polarity reversing switches since all of the current tothe electrode is passed through a single set of switches. U.S. Pat. No.6,291,798 does show a master and slave combination of power supplies fora single electrode and discloses general background information to whichthe invention is directed. For that reason, this patent is alsoincorporated by reference as though fully set forth herein. Animprovement for operating tandem electrodes with controlled switchingpoints is disclosed in Houston U.S. Pat. No. 6,472,634. This patent isincorporated by reference.

The tandem electrodes of the present invention have two leadingelectrodes as disclosed in Shutt U.S. Pat. No. 4,246,463 and in apublication by The Lincoln Electric Company of Cleveland, Ohio entitled“Another Arc Welding Development.” These items showing a modified serieslead electrode revision of a tandem arc welder, i.e. welder system, areincorporated by reference herein as background technology which need notbe revisited.

BACKGROUND OF INVENTION

Welding applications, such as pipe and plate welding, often require highcurrents and use several arcs created by tandem electrodes. Such weldingsystems are quite prone to certain inconsistencies caused by arcdisturbances due to magnetic interaction between two adjacent tandemelectrodes. A system for correcting the disadvantages caused by adjacentAC driven tandem electrodes is disclosed in Stava U.S. Pat. No.6,207,929. In that prior patent, each of the AC driven electrodes hasits own inverter based power supply. The output frequency of each powersupply is varied so as to prevent interference between adjacentelectrodes. This system requires a separate power supply for eachelectrode. As the current demand for a given electrode exceeds thecurrent rating of the inverter based power supply, a new power supplymust be designed, engineered and manufactured. Thus, such system foroperating tandem welding electrodes require high capacity or high ratedpower supplies to obtain high current as required for pipe welding. Todecrease the need for special high current rated power supplies fortandem operated electrodes, assignee developed the system disclosed inStava U.S. Pat. No. 6,291,798 wherein each AC electrode is driven by twoor more inverter power supplies connected in parallel. These parallelpower supplies have their output current combined at the input side of apolarity switching network. Thus, as higher currents are required for agiven electrode, two or more parallel power supplies are used. In thissystem, each of the power supplies is operated in unison and shareequally the output current. Thus, the current required by changes in thewelding conditions can be provided only by the over current rating of asingle unit. A current balanced system did allow for the combination ofseveral smaller power supplies; however, the power supplies had to beconnected in parallel on the input side of the polarity reversingswitching network. As such, large switches were required for eachelectrode. Consequently, such system overcame the disadvantage ofrequiring special power supplies for each electrode in a tandem weldingoperation of the type used in pipe welding; but, there is still thedisadvantage that the switches must be quite large and the input,paralleled power supplies must be accurately matched by being drivenfrom a single current command signal. Stava U.S. Pat. No. 6,291,798 doesutilize the concept of a synchronizing signal for each welding celldirecting current to each tandem electrode. However, the system stillrequired large switches. This type of system was available for operationin an ethernet network interconnecting the welding cells. In ethernetinterconnections, the timing cannot be accurately controlled. In thesystem described, the switch timing for a given electrode need only beshifted on a time basis, but need not be accurately identified for aspecific time. Thus, the described system requiring balancing thecurrent and a single switch network has been the manner of obtaininghigh capacity current for use in tandem arc welding operations whenusing an ethernet network or an internet and ethernet control system.There is a desire to control welders by an ethernet network, with orwithout an internet link. Due to timing limitation, these networksdictated use of tandem electrode systems of the type using only generalsynchronizing techniques.

Such systems could be controlled by a network; however, the parameter toeach paralleled power supply could not be varied. Each of the cellscould only be offset from each other by a synchronizing signal. Suchsystems were not suitable for central control by the internet and/orlocal area network control because an elaborate network to merelyprovide offset between cells was not advantageous. Houston U.S. Pat. No.6,472,634 discloses the concept of a single AC arc welding cell for eachelectrode wherein the cell itself includes one or more paralleled powersupplies each of which has its own switching network. The output of theswitching network is then combined to drive the electrode. This allowsthe use of relatively small switches for polarity reversing of theindividual power supplies paralleled in the system. In addition,relatively small power supplies can be paralleled to build a highcurrent input to each of several electrodes used in a tandem weldingoperation. The use of several independently controlled power suppliesparalleled after the polarity switch network for driving a singleelectrode allows advantageous use of a network, such as the internet orethernet.

In Houston U.S. Pat. No. 6,472,634, smaller power supplies in eachsystem is connected in parallel to power a single electrode. Bycoordinating switching points of each paralleled power supply with ahigh accuracy interface, the AC output current is the sum of currentsfrom the paralleled power supplies without combination before thepolarity switches. By using this concept, the ethernet network, with orwithout an internet link, can control the weld parameters of eachparalleled power supply of the welding system. The timing of the switchpoints is accurately controlled by the novel interface, whereas the weldparameters directed to the controller for each power supply can beprovided by an ethernet network which has no accurate time basis. Thus,an internet link can be used to direct parameters to the individualpower supply controllers of the welding system for driving a singleelectrode. There is no need for a time based accuracy of these weldparameters coded for each power supply. In the preferred implementation,the switch point is a “kill” command awaiting detection of a currentdrop below a minimum threshold, such as 100 amperes. When each powersupply has a switch command, then they switch. The switch points betweenparallel power supplies, whether instantaneous or a sequence involving a“kill” command with a wait delay, are coordinated accurately by aninterface card having an accuracy of less than 10 μs and preferably inthe range of 1-5 μs. This timing accuracy coordinates and matches theswitching operation in the paralleled power supplies to coordinate theAC output current.

By using the internet or ethernet local area network, the set of weldparameters for each power supply is available on a less accurateinformation network, to which the controllers for the paralleled powersupplies are interconnected with a high accuracy digital interface card.Thus, the switching of the individual, paralleled power supplies of thesystem is coordinated. This is an advantage allowing use of the internetand local area network control of a welding system. The informationnetwork includes synchronizing signals for initiating several arcwelding systems connected to several electrodes in a tandem weldingoperation in a selected phase relationship. Each of the welding systemsof an electrode has individual switch points accurately controlled whilethe systems are shifted or delayed to prevent magnetic interferencebetween different electrodes. This allows driving of several ACelectrodes using a common information network. The Houston U.S. Pat. No.6,472,634 system is especially useful for paralleled power supplies topower a given electrode with AC current. The switch points arecoordinated by an accurate interface and the weld parameter for eachparalleled power supply is provided by the general information network.This background is technology developed and patented by assignee anddoes not necessarily constitute prior art just because it is herein usedas “background.”

As a feature of the system in Stava U.S. Pat. No. 6,207,929, two or morepower supplies can drive a single electrode. Thus, the system comprisesa first controller for a first power supply to cause the first powersupply to create an AC current between the electrode and workpiece bygenerating a switch signal with polarity reversing switching points ingeneral timed relationship with respect to a given system synchronizingsignal received by the first controller. This first controller isoperated at first welding parameters in response to a set of first powersupply specific parameter signals directed to the first controller.There is provided at least one slave controller for operating the slavepower supply to create an AC current between the same electrode andworkpiece by reversing polarity of the AC current at switching points.The slave controller operates at second weld parameters in response tothe second set of power supply specific parameter signals to the slavecontroller. An information network connected to the first controller andthe second or slave controller contains digital first and second powersupply specific parameter signals for the two controllers and the systemspecific synchronizing signal. Thus, the controllers receive theparameter signals and the synchronizing signal from the informationnetwork, which may be an ethernet network with or without an internetlink, or merely a local area network. The invention involves a digitalinterface connecting the first controller and the slave controller tocontrol the switching points of the second or slave power supply by theswitch signal from the first or master controller. In practice, thefirst controller starts a current reversal at a switch point. This eventis transmitted at high accuracy to the slave controller to start itscurrent reversal process. When each controller senses an arc currentless than a given number, a “ready signal” is created. After a “ready”signal from all paralleled power supplies, all power supplies reversepolarity. This occurs upon receipt of a strobe or look command each 25μs. Thus, the switching is in unison and has a delay of less than 25 μs.Consequently, both of the controllers have interconnected datacontrolling the switching points of the AC current to the singleelectrode. The same controllers receive parameter information and asynchronizing signal from an information network which in practicecomprises a combination of internet and ethernet or a local areaethernet network. The timing accuracy of the digital interface is lessthan about 10 μs and, preferably, in the general range of 1-5 μs. Thus,the switching points for the two controllers driving a single electrodeare commanded within less than 5 μs. Then, switching actually occurswithin 25 μs. At the same time, relatively less time sensitiveinformation is received from the information network also connected tothe two controllers driving the AC current to a single electrode in atandem welding operation. The 25 μs maximum delay can be changed, but isless than the switch command accuracy.

The unique control system disclosed in Houston U.S. Pat. No. 6,472,634is used to control the power supply for tandem electrodes used primarilyin pipe seam welding and disclosed in Stava U.S. Pat. No. 6,291,798.This Stava patent relates to a series of tandem electrodes movable alonga welding path to lay successive welding beads in the space between theedges of a rolled pipe or the ends of two adjacent pipe sections. Theindividual AC waveforms used in this unique technology are created by anumber of current pulses occurring at a frequency of at least 18 kHzwith a magnitude of each current pulse controlled by a wave shaper. Thistechnology dates back to Blankenship U.S. Pat. No. 5,278,390. Shaping ofthe waveforms in the AC currents of two adjacent tandem electrodes isknown and is shown in not only the patents mentioned above, but in StavaU.S. Pat. No. 6,207,929. In this latter Stava patent, the frequency ofthe AC current at adjacent tandem electrodes is adjusted to preventmagnetic interference. All of these patented technologies by The LincolnElectric Company of Cleveland, Ohio have been advances in the operationof tandem electrodes each of which is operated by a separate AC waveformcreated by the waveform technology set forth in these patents. Thesepatents are incorporated by reference herein in their entirety. However,these patents do not disclose the present invention which is directed tothe use of such waveform technology for use in tandem welding byadjacent electrodes each using an AC current. This technology, as thenormal transformer technology, has experienced difficulty in controllingthe dynamics of the weld puddle. Thus, there is a need for an electricarc welding system for adjacent tandem electrodes which is specificallydesigned to control the dynamics and physics of the molten weld puddleduring the welding operation. These advantages can not be obtained bymerely changing the frequency to reduce the magnetic interference.

To control penetration by the lead electrode in tandem electric arcwelding or welding system, a unique leading electrode arrangement hasbeen used for a number of years. The initial concept involved two movinglead electrodes connected to the power source in a series so currentwould flow from the tip of one electrode to the tip of the adjacentelectrode. Both of these electrodes were movable toward a common pointat the weld puddle in the groove between the edges of the workpiecebeing welded. By using a series arrangement, one electrode was connectedto the work terminal of the power source and the other was connected tothe normal electrode terminal. All of the power was between theelectrodes and not between the electrode and the workpiece.Consequently, there was essentially zero arc force. The electrodes weremelted by the current flow between the electrodes. This provided adouble deposition rate with a substantially reduced heat input to theweld puddle. The heat to the puddle was, thus, decreased. Thedisadvantage of the series electrode concept was that there was verylittle penetration. The arc did not extend to the workpiece. The metalwas deposited into the joint between the edges of the workpieceprimarily by gravity. To increase the penetration of the lead arc by thetwo series electrodes, the trailing electrode was also connected tomachine ground. This concept is disclosed in Shutt U.S. Pat. No.4,246,463. In this arrangement, the arc traveled between the twoelectrodes and from the lead electrode to the workpiece. With two 3/16inch electrodes, the modified series arc system had the current from thelead electrode flowing through two paths back to the power source. Thecurrent either passed to the trailing electrode or to the workpiece. Inpractice, the ratio of current flow from the lead electrode back to thepower source is approximately ⅓ through the work and ⅔ through theelectrode. The work had substantially more resistance in the returnparallel circuit. This arrangement doubled the deposition rate. Theamount of current into the plate or workpiece was about 30% of the totalcurrent of the welding operation. Consequently, there was doubledeposition rate and decreased heat into the plate. Penetration wascaused by the modified series circuit connection of the two leadelectrodes. This single side welding of heavy workpieces has not beenused extensively because the frequency of the AC current in the seriesconnected electrodes was controlled by the line frequency of the powersource. The wire feeder for each of the electrodes was controlled by thesame power source. This limited the relationship of the two motorsdriving the wire feeders. The input voltage and frequency of the powersource was used to drive both wire feeders. Consequently, using theprior art system with all of its apparent advantages could beaccomplished in only a relatively small range of currents and with onlycertain limited electrode sizes. Thus, using the prior art system wasrestricted. There had to be a tuning of the current and input frequencyfor proper melting, penetration and wire feed speed. The parameters ofthe power source and the interrelationship of the two independentlydriven wire feeders rendered the advantageous prior welding technique ofa tandem arc welder where the two electrodes are connected in series anddriven by AC current to be quite limited. Since there is a limitedapplication of this technology, it was not possible to sell seriesconnected tandem electrode equipment for general purpose electric arcwelding. Consequently, the advantages of modified series connectedelectrodes in a tandem welding system has essentially lay dormantthrough the many years of its existence.

SUMMARY OF THE INVENTION

To render universally acceptable and usable, a tandem electric arcwelder or system having two lead electrodes connected in a modifiedseries circuit, the present invention was developed. By usingembodiments of the present invention, large plates can be welded fromone side in a submerged arc welding operation, with an arc force causingpenetration while the series connected electrodes substantially increasethe deposition. By using embodiments of the present invention, a rootweld bead is deposited by the two series connected lead electrodes. Thisjoins the two spaced edges of the workpiece together. In practice thelarge plates are ship sheet plates or the ends of pipe segments in pipewelding. Embodiments of the present invention modify the well knownseries connected lead electrode concept for tandem welding so that sucha welder can be used with a large variety of currents and a largevariety of electrodes, both size and material. This is a substantialadvance in the electric arc welding field and solves the reason for thelack of use of the modified series connected tandem electrodes in oneside, submerged arc welding. The modification can be used in other typesof welding.

In accordance with embodiments of the present invention, there isprovided an electric arc welder for depositing weld metal along thegroove between edges of a metal workpiece. The welder comprises anelectrode driven by the wire feeder toward a point in the groove. Asecond electrode is driven by a second wire feeder toward the same pointin the groove. A main power source is connected to the electrode with afirst output terminal of the power source connected to the firstelectrode and a second output terminal of the main power sourceconnected to both the second electrode and directly or indirectly to themetal workpiece. The welder includes two return paths, one through thesecond electrode and one through the workpiece. The power sourceincludes a high speed switching output stage such as an inverterchopper. This stage creates current with a selected AC waveform betweenthe first and second output terminals of the main power source. Thewaveform of the main power source is generated by a waveform generatorcontrolling a pulse width modulator circuit normally a digital circuit,but in some instances it is an analog PWM circuit. The pulse widthmodulator circuit, digital or analog, determines the current operationof the output stage of the main power source. A device is used to movethe electrodes in unison along the groove in a given direction. Theseelectrodes form the lead electrodes in a tandem electrode arc welder orelectric arc welding system. In accordance with an exemplary embodimentof the present invention, a third, fourth or fifth electrode isconnected behind the first and second series connected electrodes. Eachof these following electrodes is movable with the first series connectedelectrodes. In practice, they are movable on the same mechanism ortractor; however, they could be moved separately and still be “generallymovable” with the first and second series connected electrodes. Thethird or subsequent electrodes are each powered by an auxiliary powersource different from the main power source, with the first outputterminal connected to the third electrode and a second output terminalconnected to the workpiece. This is a standard connection for thetrailing electrodes of a tandem welding operation.

Still a further aspect of the present invention is the provision of anelectric arc welder as defined above wherein the auxiliary power sourcefor the tailing electrodes also includes a high speed switching outputstage, such as an inverter or chopper. This output stage creates aselected trailing waveform between the first and second output terminalsof the auxiliary power source. The trailing waveform of the auxiliarypower source is generated by a waveform generator controlling the pulsewidth modulator circuit, either digital or analog, to determine thecurrent operation of the output stage of the auxiliary power source. Thenumber of power sources, as shown in the prior art, can vary accordingto the number of trailing electrodes. Indeed, one power source canoperate two trailing electrodes or two power sources can operate asingle trailing electrode. These are all variations used in tandemelectric arc welding as defined in the various patents incorporated byreference herein.

In accordance with an aspect of the invention, the trailing waveforms ofthe trailing electrodes are also an AC waveform, such as used in theseries connected lead electrodes of the electric welder constructed inaccordance with aspects of the present invention. Of course, thetrailing electrodes could have waveforms which are DC waveforms createdby the waveform generator producing a steady output signal fordetermining the magnitude of the DC waveform. In this instance, waveformis a level of current, whereas “waveform” is used in this applicationprimarily to mean a repeating AC waveform.

In accordance with another aspect of the present invention, the mainpower source includes a first and second module power source connectedin parallel with the output terminals of the main power source. Toprovide greater current, a second module is connected in parallel with afirst module. The two power source modules are defined as the “main”power source driving the series connected lead electrodes of the presentinvention. In an exemplary implementation, a second power source isconnected in series between the second electrode and the workpiece. Inthis arrangement, one terminal of the main power source and a terminalof the second power source are connected in series and to the secondelectrode. The second power source is in the workpiece path. By usingtwo power sources, the separate independently driven wire feeders forthe two series connected electrodes can be controlled by different powersources. This prevents a complicated software development when a singlepower source is used to drive the separate two wire feeders used for thelead electrodes of the invention. Consequently, there is an advantage ofusing two separate power sources, with each of the power sources havinga wire feed control circuit that can be adjusted to optimize the wirefeeder of each of the series connected electrodes forming the leadelectrodes of the tandem welding system obtained by the presentinvention.

Embodiments of the present invention are primarily used for one sidedwelding on large plates. In this context, the invention also includesthe concept of a back plate below the groove accepting the weld metal.The back plate is on the underside of the workpiece and normallyprovides a trough with flux that controls the backside weld beadconfiguration. In accordance with an aspect, there is a flux dispenserin front of the trailing electrodes. Thus, the trailing electrodes areused for submerged arc welding. In practice, the first series electrodesare either gas shielded or provided with a flux dispenser to create asubmerged arc welding process for the first two electrodes.

By using embodiments of the present invention, the waveform generatorfor the main power source is provided with a circuit to adjust thefrequency of the AC waveform between the series connected leadelectrodes. In this manner, the frequency of the AC waveform used in theseries connected electrodes is not dictated in any fashion by thefrequency of line voltage to the main power source. By adjusting thefrequency of the waveform, the welding operation for the seriesconnected electrodes can be modulated to accommodate different diameterelectrodes, electrodes with different material and a variety of currentsto customize the welding operation in a manner not available in theprior art. Furthermore, the waveform generator of the present inventionhas a circuit for adjusting duty cycles of the AC waveforms from themain power source. Thus, the welding operation can be adjusted betweenpenetration and deposition to customize the operation of the weldprocess. To accomplish this objective, the magnitude of the positivecurrent portion of the waveform are controlled independently or as apercentage of the magnitude of the negative portion of the AC waveform.All of these adjustment circuits allow the main power source to beadjusted in frequency, duty cycle and/or amplitudes to customize thewelder for providing an optimized welding process, while still employingthe tremendously advantageous series connected electrodes.

A primary object of embodiments of the present invention is theprovision of a tandem electric arc welder wherein the lead electrodesare connected in series, which welder includes an AC current waveform inthe two series connected electrodes, which waveform can be adjusted tocustomize the welding operation performed by the lead electrodes in thetandem electrode welder.

Another object of embodiments of the present invention is the provisionof an electric arc welder, as defined above, which electric arc weldercan use different electrodes and different current settings to performthe AC arc welding process with the series connected lead electrodes.

Yet another object of embodiments of the present invention is theprovision of an electric arc welder, as defined above, which electricarc welder has the capabilities of adjusting the frequency of thewaveform, the duty cycle of the waveform and/or the magnitude of thecurrent in the positive and negative portions of the waveform so thatthe welding process performed by the lead series connected electrodesare customized.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The above and/or other aspects of the invention will be more apparent bydescribing in detail exemplary embodiments of the invention withreference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a welder used to practice an exemplaryembodiment of the present invention;

FIG. 2 is a wiring diagram of two paralleled power supplies, each ofwhich include a switching output which power supplies;

FIG. 3 is a cross sectional side view of three tandem electrodes forwelding the seam of a pipe;

FIG. 4 is a schematic layout in block form of a welding system for threeelectrodes using the disclosure in Houston U.S. Pat. No. 6,472,634 andStava U.S. Pat. No. 6,291,798;

FIG. 5 is a block diagram showing a single electrode driven by thesystem as shown in FIG. 4 with a variable pulse generator disclosed inHouston U.S. Pat. No. 6,472,634;

FIG. 6 is a current graph for one of two illustrated synchronizingpulses and showing a balanced AC waveform for one tandem electrode;

FIG. 7 is a current graph superimposed upon a signal having logic todetermine the polarity of the waveform as used in practicing embodimentsof the present invention;

FIG. 8 is a current graph showing a broad aspect of waveforms used in anexemplary embodiment of the present invention;

FIGS. 9 and 10 are schematic drawings illustrating the dynamics of theweld puddle during concurrent polarity relationships of tandemelectrodes;

FIG. 11 is a pair of current graphs showing the waveforms on twoadjacent tandem electrodes;

FIG. 12 is a pair of current graphs of the AC waveforms on adjacenttandem electrodes with areas of concurring polarity relationships;

FIG. 13 are current graphs of the waveforms on adjacent tandemelectrodes wherein the AC waveform of one electrode is substantiallydifferent waveform of the other electrode to limit the time ofconcurrent polarity relationships;

FIG. 14 are current graphs of two sinusoidal waveforms for adjacentelectrodes to use different shaped wave forms for the adjacent tandemelectrodes;

FIG. 15 are current graphs showing waveforms at four adjacent AC arcs oftandem electrodes shaped and synchronized in accordance with the welderconstructed in accordance with an exemplary embodiment of the invention;

FIG. 16 is a schematic layout of the software program to cause switchingof the paralleled power supplies as soon as the coordinated switchcommands have been processed and the next coincident signal has beencreated;

FIG. 17 is a schematic view of the general architecture of an exemplaryembodiment of the present invention;

FIG. 18 is a partial cross-sectional view taken generally along line18-18 of FIG. 17;

FIG. 19 is a schematic layout of the software program, together with ablock diagram schematically illustrating the operation of the main powersource used in an exemplary embodiment of the present invention;

FIG. 20 is a partial side elevational view of an exemplary embodiment ofthe present invention illustrating only the lead series connectedelectrode used in the present invention with a modification of the mainpower source;

FIG. 21 is a view similar to FIG. 20 showing an exemplary embodiment andpractical embodiment now used for the main power source and theworkpiece path of the present invention;

FIG. 22 is a schematic view of another exemplary embodiment of thepresent invention;

FIG. 23 is a schematic view of a carriage assembly of welding contactsin accordance with an embodiment of the present invention;

FIG. 24 is another schematic view of an exemplary embodiment of thepresent invention;

FIGS. 25 and 26 are graphs depicting wave balance;

FIG. 27 is a graph depicting current offset; and

FIG. 28 is a graph depicting phase angle shift.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposeof illustrating exemplary embodiments of the invention only and not forthe purpose of limiting the same, a system used in practicing theinvention is shown in detail in FIGS. 1, 2 and 16. In FIG. 1 there is asingle electric arc welding system S in the form of a single cell tocreate an alternating current as an are at weld station WS. This systemor cell includes a first master welder A with output leads 10, 12 inseries with electrode E and workpiece W in the form of a pipe seam jointor other welding operation. Hall effect current transducer 14 provides avoltage in line 16 proportional to the current of welder A. Less timecritical data, such as welding parameters, are generated at a remotecentral control 18. In a like manner, a slave following welder Bincludes leads 20, 22 connected in parallel with leads 10, 12 to directan additional AC current to the weld station WS. Hall effect currenttransducer 24 creates a voltage in line 26 representing current levelsin welder B during the welding operation. Even though a single slave orfollower welder B is shown, any number of additional welders can beconnected in parallel with master welder A to produce an alternatingcurrent across electrode E and workpiece W. The AC current is combinedat the weld station instead of prior to a polarity switching network.Each welder includes a controller and inverter based power supplyillustrated as a combined master controller and power supply 30 and aslave controller and power supply 32. Controllers 30, 32 receiveparameter data and synchronization data from a relatively low levellogic network. The parameter information or data is power supplyspecific whereby each of the power supplies is provided with the desiredparameters such as current, voltage and/or wire feed speed. A low leveldigital network can provide the parameter information; however, the ACcurrent for polarity reversal occurs at the same time. The “same” timeindicates a time difference of less than 10 μs and preferably in thegeneral range of 1-5 μs. To accomplish precise coordination of the ACoutput from power supply 30 and power supply 32, the switching pointsand polarity information can not be provided from a general logicnetwork wherein the timing is less precise. The individual AC powersupplies are coordinated by high speed, highly accurate DC logicinterface referred to as “gateways.” As shown in FIG. 1, power supplies30, 32 are provided with the necessary operating parameters indicated bythe bi-directional leads 42 m, 42 s, respectively. This non-timesensitive information is provided by a digital network shown in FIG. 1.Master power supply 30 receives a synchronizing signal as indicated byunidirectional line 40 to time the controllers operation of its ACoutput current. The polarity of the AC current for power supply 30 isoutputted as indicated by line 46. The actual switching command for theAC current of master power supply 30 is outputted on line 44. The switchcommand tells power supply S, in the form of an inverter, to “kill,”which is a drastic reduction of current. In an alternative, this isactually a switch signal to reverse polarity. The “switching points” orcommand on line 44 preferably is a “kill” and current reversal commandsutilizing the “switching points” as set forth in Stava U.S. Pat. No.6,111,216. Thus, timed switching points or commands are outputted frompower supply 30 by line 44. These switching points or commands mayinvolve a power supply “kill” followed by a switch ready signal at a lowcurrent or merely a current reversal point. The switch “ready” is usedwhen the “kill” concept is implemented because neither inverters are toactually reverse until they are below the set current. This is describedin FIG. 16. The polarity of the switches of controller 30 controls thelogic on line 46. Slave power supply 32 receives the switching point orcommand logic on line 44 b and the polarity logic on line 46 b. Thesetwo logic signals are interconnected between the master power supply andthe slave power supply through the highly accurate logic interface shownas gateway 50, the transmitting gateway, and gateway 52, the receivinggateway on lines 44 a, 46 a. These gateways are network interface cardsfor each of the power supplies so that the logic on lines 44 b, 46 b aretimed closely to the logic on lines 44, 46, respectively. In practice,network interface cards or gateways 50, 52 control this logic to within10 μs and preferably within 1-5 μs. A low accuracy network controls theindividual power supplies for data from central control 18 through lines42 m, 42 s, illustrated as provided by the gateways or interface cards.These lines contain data from remote areas (such as central control 18)which are not time sensitive and do not use the accuracy characteristicsof the gateways. The highly accurate data for timing the switch reversaluses interconnecting logic signals through network interface cards 50,52. The system in FIG. 1 is a single cell for a single AC arc; however,embodiments of the invention are directed to tandem electrodes whereintwo or more AC arcs are created to fill the large gap found in pipewelding. Thus, the master power supply 30 for the first electrodereceives a synchronization signal which determines the timing or phaseoperation of the system S for a first electrode, i.e. ARC 1. System S isused with other identical systems to generate ARCs 2, 3, and 4 timed bysynchronizing outputs 84, 86 and 88. This concept is schematicallyillustrated in FIG. 5. The synchronizing or phase setting signals 82-88are shown in FIG. 1 with only one of the tandem electrodes. Aninformation network N comprising a central control computer and/or webserver 60 provides digital information or data relating to specificpower supplies in several systems or cells controlling differentelectrodes in a tandem operation. Internet information 62 is directed toa local area network in the form of an ethernet network 70 having localinterconnecting lines 70 a, 70 b, 70 c. Similar interconnecting linesare directed to each power supply used in the four cells creating ARCs1, 2, 3 and 4 of a tandem welding operation. The description of systemor cell S applies to each of the arcs at the other electrodes. If ACcurrent is employed, a master power supply is used. In some instances,merely a master power supply is used with a cell specific synchronizingsignal. If higher currents are required, the systems or cells include amaster and slave power supply combination as described with respect tosystem S of FIG. 1. In some instances, a DC arc is used with two or moreAC arcs synchronized by generator 80. Often the DC arc is the leadingelectrode in a tandem electrode welding operation, followed by two ormore synchronized AC arcs. A DC power supply need not be synchronized,nor is there a need for accurate interconnection of the polarity logicand switching points or commands. Some DC powered electrodes may beswitched between positive and negative, but not at the frequency of anAC driven electrode. Irrespective of the make-up of the arcs, ethernetor local area network 70 includes the parameter information identifiedin a coded fashion designated for specific power supplies of the varioussystems used in the tandem welding operation. This network also employssynchronizing signals for the several cells or systems whereby thesystems can be offset in a time relationship. These synchronizingsignals are decoded and received by a master power supply as indicatedby line 40 in FIG. 1. In this manner, the AC arcs are offset on a timebasis. These synchronizing signals are not required to be as accurate asthe switching points through network interface cards or gateways 50, 52.Synchronizing signals on the data network are received by a networkinterface in the form of a variable pulse generator 80. The generatorcreates offset synchronizing signals in lines 84, 86 and 88. Thesesynchronizing signals dictate the phase of the individual alternatingcurrent cells for separate electrodes in the tandem operation.Synchronizing signals can be generated by interface 80 or actuallyreceived by the generator through the network 70. In practice, network70 merely activates generator 80 to create the delay pattern for themany synchronizing signals. Also, generator 80 can vary the frequency ofthe individual cells by frequency of the synchronizing pulses if thatfeature is desired in the tandem welding operation.

A variety of controllers and power supplies could be used for practicingthe system as described in FIG. 1; however, exemplary implementation ofthe system is set forth in FIG. 2 wherein power supply PSA is combinedwith controller and power supply 30 and power supply PSB is combinedwith controller and power supply 32. These two units are essentially thesame in structure and are labeled with the same numbers whenappropriate. Description of power supply PSA applies equally to powersupply PSB. Inverter 100 has an input rectifier 102 for receiving threephase line current L1, L2, and L3. Output transformer 110 is connectedthrough an output rectifier 112 to tapped inductor 120 for drivingopposite polarity switches Q1, Q2. Controller 140 a of power supply PSAand controller 140 b of PSB are essentially the same, except controller140 a outputs timing information to controller 140 b. Switching pointsor lines 142, 144 control the conductive condition of polarity switchesQ1, Q2 for reversing polarity at the time indicated by the logic onlines 142, 144, as explained in more detail in Stava U.S. Pat. No.6,111,216 incorporated by reference herein. The control is digital witha logic processor; thus, A/D converter 150 converts the currentinformation on feedback line 16 or line 26 to controlling digital valuesfor the level of output from error amplifier 152 which is illustrated asan analog error amplifier. In practice, this is a digital system andthere is no further analog signal in the control architecture. Asillustrated, however, amplifier has a first input 152 a from converter150 and a second input 152 b from controller 140 a or 140 b. The currentcommand signal on line 152 b includes the wave shape or waveformrequired for the AC current across the arc at weld station WS. This isstandard practice as taught by several patents of Lincoln Electric, suchas Blankenship U.S. Pat. No. 5,278,390, incorporated by reference. Seealso Stava U.S. Pat. No. 6,207,929, incorporated by reference. Theoutput from amplifier 152 is converted to an analog voltage signal byconverter 160 to drive pulse width modulator 162 at a frequencycontrolled by oscillator 164, which is a timer program in the processorsoftware. The shape of the waveform at the arcs is the voltage ordigital number at lines 152 b. The frequency of oscillator 164 isgreater than 18 kHz. The total architecture of this system is digitizedin the preferred embodiment of the present invention and does notinclude reconversion back into analog signal. This representation isschematic for illustrative purposes and is not intended to be limitingof the type of power supply used in practicing the present invention.Other power supplies could be employed.

The practice of embodiments of the present invention utilizing theconcepts of FIGS. 1 and 2 are illustrated in FIGS. 3 and 4. Workpiece200 is a seam in a pipe which is welded together by tandem electrodes202, 204 and 206 powered by individual power supplies PS1, PS2, PS3,respectively. The power supplies can include more than one power sourcecoordinated in accordance with the technology in Houston U.S. Pat. No.6,472,634. The illustrated embodiment involves a DC arc for leadelectrode 202 and an AC arc for each of the tandem electrodes 204, 206.The created waveforms of the tandem electrodes are AC currents andinclude shapes created by a wave shaper or wave generator in accordancewith the previously described waveform technology. As electrodes 202,204 and 206 are moved along weld path WP a molten metal puddle P isdeposited in pipe seam 200 with an open root portion 210 followed bydeposits 212, 214 and 216 from electrodes 202, 204 and 206,respectively. As previously described more than two AC driven electrodesas will be described and illustrated by the waveforms of FIG. 15, can beoperated by the invention relating to AC currents of adjacentelectrodes. The power supplies, as shown in FIG. 4, each include aninverter 220 receiving a DC link from rectifier 222. In accordance withLincoln waveform technology, a chip or internal programmed pulse widthmodulator stage 224 is driven by an oscillator 226 at a frequencygreater than 18 kHz and preferably greater than 20 kHz. As oscillator226 drives pulse width modulator 224, the output current has a shapedictated by the wave shape outputted from wave shaper 240 as a voltageor digital numbers at line 242. Output leads 217, 218 are in series withelectrodes 202, 204 and 206. The shape in real time is compared with theactual arc current in line 232 from Hall Effect transducer 228 by astage illustrated as comparator 230 so that the outputs on line 234controls the shape of the AC waveforms. The digital number or voltage online 234 determines the output signal on line 224 a to control inverter220 so that the waveform of the current at the arc follows the selectedprofile outputted from wave shaper 240. This is standard Lincolnwaveform technology, as previously discussed. Power supply PS1 creates aDC arc at lead electrode 202; therefore, the output from wave shaper 240of this power supply is a steady state indicating the magnitude of theDC current. Some embodiments of the present invention do not relate tothe formation of a DC arc. To the contrary, the present invention is thecontrol of the current at two adjacent AC arcs for tandem electrodes,such as electrodes 204, 206. In accordance with the invention, waveshaper 240 involves an input 250 employed to select the desired shape orprofile of the AC waveform. This shape can be shifted in real time by aninternal programming schematically represented as shift program 252.Wave shaper 240 has an output which is a priority signal on line 254. Inpractice, the priority signal is a bit of logic, as shown in FIG. 7.Logic 1 indicates a negative polarity for the waveform generated by waveshaper 240 and logic 0 indicates a positive polarity. This logic signalor bit controller 220 directed to the power supply is read in accordancewith the technology discussed in FIG. 16. The inverter switches from apositive polarity to a negative polarity, or the reverse, at a specific“READY” time initiated by a change of the logic bit on line 254. Inpractice, this bit is received from variable pulse generator 80 shown inFIG. 1 and in FIG. 5. The welding system shown in FIGS. 3 and 4 is usedin practicing aspects of the invention wherein the shape of AC arccurrents at electrodes 204 and 206 have novel shapes to obtain abeneficial result of the present invention, i.e. a generally quiescentmolten metal puddle P and/or synthesized sinusoidal waveforms compatiblewith transformer waveforms used in arc welding. The electric arc weldingsystem shown in FIGS. 3 and 4 have a program to select the waveform at“SELECT” program 250 for wave shaper 240. In this manner the uniquewaveforms of the present invention are used by the tandem electrodes.One of the power supplies to create an AC arc is schematicallyillustrated in FIG. 5. The power supply or source is controlled byvariable pulse generator 80, shown in FIG. 1. Signal 260 from thegenerator controls the power supply for the first arc. This signalincludes the synchronization of the waveform together with the polaritybit outputted by the wave shaper 240 on line 254. Lines 260 a-260 ncontrol the desired subsequent tandem AC arcs operated by the weldingsystem of the present invention. The timing of these signals shifts thestart of the other waveforms. FIG. 5 merely shows the relationship ofvariable pulse generator 80 to control the successive arcs as explainedin connection with FIG. 4.

In the welding system of Houston U.S. Pat. No. 6,472,634, the ACwaveforms are created as shown in FIG. 6 wherein the wave shaper for arcAC1 at electrode 204 creates a signal 270 having positive portions 272and negative portions 274. The second arc AC2 at electrode 206 iscontrolled by signal 280 from the wave shaper having positive portions282 and negative portions 284. These two signals are the same, but areshifted by the signal from generator 80 a distance x, as shown in FIG.6. The waveform technology created current pulses or waveforms at one ofthe arcs are waveforms having positive portions 290 and negativeportions 292 shown at the bottom portion of FIG. 6. A logic bit from thewave shaper determines when the waveform is switched from the positivepolarity to the negative polarity and the reverse. In accordance withthe disclosure in Stava U.S. Pat. No. 6,111,216 (incorporated byreference herein) pulse width modulator 224 is generally shifted to alower level at point 291 a and 291 b. Then the current reduces untilreaching a fixed level, such as 100 amps. Consequently, the switcheschange polarity at points 294 a and 294 b. This produces a vertical lineor shape 296 a, 296 b when current transitioning between positiveportion 290 and negative portion 292. This is the system disclosed inthe Houston patent where the like waveforms are shifted to avoidmagnetic interference. The waveform portions 290, 292 are the same atarc AC1 and at arc AC2. This is different from the present inventionwhich relates to customizing the waveforms at arc AC1 and arc AC2 forpurposes of controlling the molten metal puddle and/or synthesizing asinusoidal wave shape in a manner not heretofore employed. Thedisclosure of FIG. 6 is set forth to show the concept of shifting thewaveforms, but not the invention which is customizing each of theadjacent waveforms. The same switching procedure to create a verticaltransition between polarities is used in an exemplary embodiment of thepresent invention. Converting from the welding system shown in FIG. 6 toan embodiment of the present invention is generally shown in FIG. 7. Thelogic on line 254 is illustrated as being a logic I in portions 300 anda logic 0 in portions 302. The change of the logic or bit numberssignals the time when the system illustrated in FIG. 16 shifts polarity.This is schematically illustrated in the lower graph of FIG. 6 at points294 a, 294 b. In accordance with aspects of the invention, wave shaper240 for each of the adjacent AC arcs has a first wave shape 310 for oneof the polarities and a second wave shape 312 for the other polarity.Each of the waveforms 310, 312 are created by the logic on line 234taken together with the logic on line 254. Thus, pulses 310, 312 asshown in FIG. 7, are different pulses for the positive and negativepolarity portions. Each of the pulses 310, 312 are created by separateand distinct current pulses 310 a, 312 a as shown. Switching betweenpolarities is accomplished as illustrated in FIG. 6 where the waveformsgenerated by the wave shaper are shown as having the general shape ofwaveforms 310, 312. Positive polarity controls penetration and negativepolarity controls deposition. In accordance with the invention, thepositive and negative pulses of a waveform are different and theswitching points are controlled so that the AC waveform at one arc iscontrolled both in the negative polarity and the positive polarity tohave a specific shape created by the output of wave shaper 240. Thewaveforms for the arc adjacent to the arc having the current shown inFIG. 7 is controlled differently to obtain the advantages of the presentinvention. This is illustrated best in FIG. 8. The waveform at arc AC 1is in the top part of FIG. 8. It has positive portions 320 shown bycurrent pulses 320 a and negative portions 322 formed by pulses 322 a.Positive portion 320 has a maximum magnitude a and width or time periodb. Negative portion 322 has a maximum magnitude d and a time or periodc. These four parameters are adjusted by wave shaper 240. In theillustrated embodiment, arc AC2 has the waveform shown at the bottom ofFIG. 8 where positive portion 330 is formed by current pulses 330 a andhas a height or magnitude a′ and a time length or period b′. Negativeportion 332 is formed by pulses 332 a and has a maximum amplitude d′ anda time length c′. These parameters are adjusted by wave shaper 240. Inaccordance with aspects of the invention, the waveform from the waveshaper on arc AC1 is out of phase with the wave shape for arc AC2. Thetwo waveforms have parameters or dimensions which are adjusted so that(a) penetration and deposition is controlled and (b) there is no longtime during which the puddle P is subjected to a specific polarityrelationship, be it a like polarity or opposite polarity. This conceptin formulating the wave shapes prevents long term polarity relationshipsas explained by the showings in FIGS. 9 and 10. In FIG. 9 electrodes204, 206 have like polarity, determined by the waveforms of the adjacentcurrents at any given time. At that instance, magnetic flux 350 ofelectrode 204 and magnetic flux 352 of electrode 206 are in the samedirection and cancel each other at center area 354 between theelectrodes. This causes the molten metal portions 360, 362 fromelectrodes 204, 206 in the molten puddle P to move together, asrepresented by arrows c. This inward movement together or collapse ofthe molten metal in puddle P between electrodes 204 will ultimatelycause an upward gushing action, if not terminated in a very short time,i.e. less than about 20 ms. As shown in FIG. 10, the opposite movementof the puddle occurs when the electrodes 204, 206 have oppositepolarities. Then, magnetic flux 370 and magnetic flux 372 areaccumulated and increased in center portion 374 between the electrodes.High forces between the electrodes causes the molten metal portions 364,366 of puddle P to retract or be forced away from each other. This isindicated by arrows r. Such outward forcing of the molten metal inpuddle P causes disruption of the weld bead if it continues for asubstantial time which is generally less than 10 ms. As can be seen fromFIGS. 9 and 10, it is desirable to limit the time during which thepolarity of the waveform at adjacent electrodes is either the samepolarity or opposite polarity. As shown in FIG. 8, like polarity andopposite polarity is retained for a very short time less than the cyclelength of the waveforms at arc AC1 and arc AC2. This positivedevelopment of preventing long term occurrence of polarity relationshipstogether with the novel concept of pulses having different shapes anddifferent proportions in the positive and negative areas combine tocontrol the puddle, control penetration and control deposition in amanner not heretofore obtainable in welding with a normal transformerpower supplies or normal use of Lincoln waveform technology.

In FIG. 11 the positive and negative portions of the AC waveform fromthe wave shaper 240 are synthesized sinusoidal shapes with a differentenergy in the positive portion as compared to the negative portion ofthe waveforms. The synthesized sine wave or sinusoidal portions of thewaveforms is novel. It allows the waveforms to be compatible withtransformer welding circuits and compatible with evaluation of sine wavewelding. In FIG. 11, waveform 370 is at arc AC1 and waveform 372 is atarc AC2. These tandem arcs utilize the AC welding current shown in FIG.11 wherein a small positive sinusoidal portion 370 a controlspenetration at arc AC1 while the larger negative portion 370 b controlsthe deposition of metal at arc AC1. There is a switching between thepolarities with a change in the logic bit, as discussed in FIG. 7.Sinusoidal waveform 370 plunges vertically from approximately 100amperes through zero current as shown in by vertical line 370 c.Transition between the negative portion 370 b and positive portion 370 aalso starts a vertical transition at the switching point causing avertical transition 370 d. In a like manner, phase shifted waveform 372of arc AC2 has a small penetration portion 372 a and a large negativedeposition portion 372 b. Transition between polarities is indicated byvertical lines 372 c and 372 d. Waveform 372 is shifted with respect towaveform 370 so that the dynamics of the puddle are controlled withoutexcessive collapsing or repulsion of the molten metal in the puddlecaused by polarities of adjacent arcs AC1, AC2. In the embodiment shownin FIG. 11, the sine wave shapes are the same and the frequencies arethe same. They are merely shifted to prevent a long term occurrence of aspecific polarity relationship.

In FIG. 12 waveform 380 is used for arc AC1 and waveform 382 is used forarc AC2. Portions 380 a, 380 b, 382 a, and 382 b are sinusoidalsynthesized and are illustrated as being of the same general magnitude.By shifting these two waveforms 900, areas of concurrent polarity areidentified as areas 390, 392, 394 and 396. By using the shiftedwaveforms with sinusoidal profiles, like polarities or oppositepolarities do not remain for any length of time. Thus, the molten metalpuddle is not agitated and remains quiescent. This advantage of theconcept of a difference in energy between the positive and negativepolarity portions of a given waveform. FIG. 12 is illustrative in natureto show the definition of concurrent polarity relationships and the factthat they should remain for only a short period of time. To accomplishthis objective, another embodiment of the present invention isillustrated in FIG. 13 wherein previously defined waveform 380 iscombined with waveform 400, shown as the sawtooth waveform of arc AC2(a) or the pulsating waveform 402 shown as the waveform for arc AC2(b).Combining waveform 380 with the different waveform 400 of a differentwaveform 402 produces very small areas or times of concurrent polarityrelationships 410, 412, 414, etc. In FIG. 14 the AC waveform generatedat one arc drastically different than the AC waveform generated at theother arc. This same concept of drastically different waveforms isillustrated in FIG. 14 wherein waveform 420 is an AC pulse profilewaveform and waveform 430 is a sinusoidal profile waveform having aboutone-half the period of waveform 420. Waveform 420 includes a smallpenetration positive portion 420 a and a large deposition portion 420 bwith straight line polarity transitions 420 c. Waveform 430 includespositive portion 430 a and negative portion 430 b with vertical polaritytransitions 430 c. By having these two different waveforms, both thesynthesized sinusoidal concept is employed for one electrode and thereis no long term concurrent polarity relationship. Thus, the molten metalin puddle P remains somewhat quiescent during the welding operation byboth arcs AC1, AC2.

In FIG. 15 waveforms 450, 452, 454 and 456 are generated by the waveshaper 240 of the power supply for each of four tandem arcs, arc AC1,arc AC2, arc AC3 and arc AC4. The adjacent arcs are aligned as indicatedby synchronization signal 460 defining when the waveforms correspond andtransition from the negative portion to the positive portion. Thissynchronization signal is created by generator 80 shown in FIG. 1,except the start pulses are aligned. In this embodiment of the inventionfirst waveform 450 has a positive portion 450 a, which is synchronizedwith both the positive and negative portion of the adjacent waveform452, 454 and 456. For instance, positive portion 450 a is synchronizedwith and correlated to positive portion 452 a and negative portion 452 bof waveform 452. In a like manner, the positive portion 452 a ofwaveform 452 is synchronized with and correlated to positive portion 454a and negative portion 454 b of waveform 454. The same relationshipexists between positive portion 454 a and the portions 456 a, 456 b ofwaveform 456. The negative portion 450 b is synchronized with andcorrelated to the two opposite polarity portions of aligned waveform452. The same timing relationship exist between negative portion 452 band waveform 454. In other words, in each adjacent arc one polarityportion of the waveform is correlated to a total waveform of theadjacent arc. In this manner, the collapse and repelling forces ofpuddle P, as discussed in connection with FIGS. 9 and 10, aredynametically controlled. One or more of the positive or negativeportions can be synthesized sinusoidal waves as discussed in connectionwith an aspect of the invention disclosed in FIGS. 11 and 12.

As indicated in FIGS. 1 and 2, when the master controller of switches isto switch, a switch command is issued to master controller 140 a ofpower supply 30. This causes a “kill” signal to be received by themaster so a kill signal and polarity logic is rapidly transmitted to thecontroller of one or more slave power supplies connected in parallelwith a single electrode. If standard AC power supplies are used withlarge snubbers in parallel with the polarity switches, the slavecontroller or controllers are immediately switched within 1-10 μs afterthe master power supply receives the switch command. This is theadvantage of the high accuracy interface cards or gateways. In practice,the actual switching for current reversal of the paralleled powersupplies is not to occur until the output current is below a givenvalue, i.e. about 100 amperes. This allows use of smaller switches.

The implementation of the switching for all power supplies for a singleAC arc uses the delayed switching technique where actual switching canoccur only after all power supplies are below the given low currentlevel. The delay process is accomplished in the software of the digitalprocessor and is illustrated by the schematic layout of FIG. 16. Whenthe controller of master power supply 500 receives a command signal asrepresented by line 502, the power supply starts the switching sequence.The master outputs a logic on line 504 to provide the desired polarityfor switching of the slaves to correspond with polarity switching of themaster. In the commanded switch sequence, the inverter of master powersupply 500 is turned off or down so current to electrode E is decreasedas read by hall effect transducer 510. The switch command in line 502causes an immediate “kill” signal as represented by line 512 to thecontrollers of paralleled slave power supplies 520, 522 providingcurrent to junction 530 as measured by hall effect transducers 532, 534.All power supplies are in the switch sequence with inverters turned offor down. Software comparator circuits 550, 552, 554 compare thedecreased current to a given low current referenced by the voltage online 556. As each power supply decreases below the given value, a signalappears in lines 560, 562, and 564 to the input of a sample and holdcircuits 570, 572, and 574, respectively. The circuits are outputted bya strobe signal in line 580 from each of the power supplies. When a setlogic is stored in a circuit 570, 572, and 574, a YES logic appears onlines READY¹, READY², and READY³ at the time of the strobe signal. Thissignal is generated in the power supplies and has a period of 25 μs;however, other high speed strobes could be used. The signals aredirected to controller C of the master power supply, shown in dashedlines in FIG. 16. A software ANDing function represented by AND gate 584has a YES logic output on line 582 when all power supplies are ready toswitch polarity. This output condition is directed to clock enableterminal ECLK of software flip flop 600 having its D terminal providedwith the desired logic of the polarity to be switched as appearing online 504. An oscillator or timer operated at about 1 MHz clocks flipflop by a signal on line 602 to terminal CK. This transfers the polaritycommand logic on line 504 to a Q terminal 604 to provide this logic inline 610 to switch slaves 520, 522 at the same time the identical logicon line 612 switches master power supply 500. After switching, thepolarity logic on line 504 shifts to the opposite polarity while masterpower supply awaits the next switch command based upon the switchingfrequency. Other circuits can be used to effect the delay in theswitching sequence; however, the illustration in FIG. 16 is the presentscheme.

Embodiments of the present application relate to the waveformscontrolled by a wave shaper or waveform generator of an electric arcpower supply including a single power source or multiple power sourcescorrelated as disclosed in Houston U.S. Pat. No. 6,472,634 or Stava U.S.Pat. No. 6,291,798. The invention relates to tandem electrodes poweredby an AC waveform. The two adjacent electrodes have waveforms thatcontrol the dynamics of the molten metal puddle between the electrodesand/or uses synthesized sine waves to correlate the operation of thetandem welding system with standard transformer welding operations.Different energy in the positive portion and negative portion controlsthe relationship of the amount of penetration to the amount ofdeposition by a particular electrode. This allows operation of adjacentelectrodes in a manner to maintain the weld puddle generally quiescent.This action improves the resulting weld bead and the efficiency of thewelding operation. To control the weld puddle, adjacent waveformsgenerated by the wave shaper have different shapes to control the lengthof time during which a given polarity relationship exist between theadjacent electrodes. In other words, the time that the waveforms ofadjacent electrodes have like polarity or opposite polarity is limitedby using different shapes and different relationships between the twoadjacent AC waveforms generated by the waveform technology using a waveshaper or waveform generator.

As so far described, the technology used in practicing embodiments ofthe present invention is explained in detail. The technology in FIGS.1-16 is employed in an exemplary embodiment of the present invention.The exemplary embodiment of the invention involves an electric arcwelder schematically illustrated in FIGS. 17 and 18 and involves tandemelectric arc welding wherein first electrode E1 and second electrode E2are connected in modified series. The subsequent electrodes, one ofwhich is illustrated as electrode E3, are driven in unison withelectrodes E1 and E2 and perform a tandem welding process. Of course,several trailing electrodes E3 are normally used. Only one trailingelectrode E3 is illustrated and the same disclosure relates to the otheranticipated trailing electrodes. The technology described in FIGS. 1-16is applicable to electric arc welder 700 used to deposit metal in groove702 of workpiece W. In the illustrated embodiment, the workpiece W isspaced plates 710, 712 with a small gap b where edges 714, 716 definetrough 704 in plate B having an angle 718, best shown in FIG. 18.Electrodes E1, E2 are arranged, as shown in FIG. 17, and are directedtoward a point in groove 704, best shown in FIG. 18. This point is belowthe electrical contact 750 and defines a stickout h. Referring now morespecifically to FIG. 17, mechanism 720 drives lead electrodes E1, E2along groove 702 and includes a main power source 722, with outputterminals 724, 726 to direct AC current by way of leads 730, 732 to therespective electrodes E1, E2. The electrodes are supplied from spool740, 742, respectively, and are driven through contacts 750, 752 bystandard wire feeders 760, 762, respectively. Wire feeder 760 includesdrive rolls 760 a, 760 b rotated by a motor 760 c. In a like manner,wire feeder 762 includes drive rolls 762 a, 762 b rotated by motor 762c. Leads 760 d and 762 d are both powered by a control signal in line764 from main power source 722. The power source is a Power Wave unitsold by The Lincoln Electric Company of Cleveland, Ohio and is generallydisclosed in Blankenship U.S. Pat. No. 5,278,390. Power source 722 isused to control both wire feeders 760, 762. This results in alimitation, since a single signal is available from the power source todrive the wire feeder. When this occurs, the signal on line 764 must bea compromise signal between the desired wire feed speed of electrodesE1, E2. In practice, the single signal on line 764 drives both wirefeeders. Of course, software could be developed for providing separatecontrols for the individual wire feeders at a substantial cost. Separatesignals for the wire feeder are created when using two power sources, asshown in FIGS. 20 and 21. Lead 732 is connected to contact 752 by line734 and to workpiece W by line 736. Thus, current flow between electrodeE1 and power source 722 is through a low resistance line 734 and ahigher resistance line 736. The resistance of these return paths dividesthe current flow to adjust the heat in the arc and penetration by thearc force in the welding process. By using the mechanism 720, highdeposition by using two series electrodes is accomplished at low heat. Alimited amount of current flows from electrode E1 into the workpieceduring the welding operation. This welding process is controllable inaccordance with the present invention, by the circuit schematicallyillustrated in FIG. 19.

In accordance with an exemplary embodiment of the invention, electrodesE1, E2 are trailed by at least one electrode E3, shown in FIG. 17. Thistrailing electrode is driven by mechanism 770 in unison with electrodesE1, E2 even though they may be moved by different mechanisms. In anexemplary embodiment, the same moving device is used for mechanisms 720,770. The trailing electrode mechanism includes auxiliary power source772 which is also a Power Wave unit manufactured by The Lincoln ElectricCompany of Cleveland, Ohio. This power source has output terminals 774,776 for directing an AC current waveform by way of lines 780, 782 to useelectrode E3 in a welding process. Electrode E3 is supplied by spool 784and is driven through contact 786 by wire feeder 790, similar to wirefeeders 760, 762. Wire feeder 790 has spaced drive rolls 790 a, 790 brotated by a motor 790. A control signal from power source 772 in line792 drives motor 790 c to feed electrode E3 toward workpiece W at aspeed determined by the signal in line 792.

In operation of the exemplary embodiment illustrated in FIGS. 17 and 18,electrodes E1, E2 and trailing electrode E3 create a weld puddle 800 ingroove 702. Electrodes E1, E2 create a first root pass 802, which beadjoins or tacks edges 714, 716 together by melting the inwardlyprojecting portions of groove 702. Thereafter, puddle 800 is enlarged byoverlaying bead 804 by trailing electrode E3. In practice, furtherelectrodes are used to fill groove 702 in a tandem welding processdisclosed in FIGS. 1-16. In practice, electrode E3 is used in asubmerged arc welding process utilizing a flux dispenser 810 in front ofelectrode E3 and having a dispensing motor 812 for dispensing flux Ffrom hopper 814 through tube 816 in accordance with standard submergedwelding technology. Of course, electrode E1, E2 also are used in asubmerged arc AC welding process. A similar flux dispenser 810 is thenprovided above groove 702 in front of electrode E1. In practice, ashielding gas has also been employed around electrodes E1, E2.Embodiments of the present invention utilize a Power Wave power sourcefor the main power source 722 and for the auxiliary power source 772.These power sources are digitally controlled and utilize a waveformtechnology pioneered by The Lincoln Electric Company whereby the powersources create waveforms that comprise a series of individual currentpulses created at a high switching speed in excess of 18 kHz andpreferably substantially greater than 20 kHz. In practice, the waveformsare provided by a series of current pulses created at a rate of over 40kHz. In this manner, the AC current of mechanism 720 and mechanism 770are provided with any AC waveform to optimize the welding process forthe lead electrodes as well as the trailing electrodes. This type ofwelding process is schematically illustrated in FIG. 19, whichrepresents the power source used in practicing the preferred embodimentof the present invention.

System 900 of the present invention is schematically illustrated in FIG.19 wherein a Power Wave power source 910 has a high switching outputstage 912 with an input rectifier 914 for receiving three phase linecurrent L1, L2, and L3, and output terminals 912 a and 912 b. Outputstage 912 creates an AC waveform at output terminals 912 a, 9112 b toperform an AC arc welding process at weld station WP illustrated asincluding electrode 920 and workpiece 922 and having a current shunt 930to output a signal in line 932. This signal represents the current ofthe welding process being performed at weld station WP. Comparator 940receives the signal on line 932 and has an output 940 a with a voltagecontrolling pulse width modulator circuit 942, which can be digital oranalog and has a variety of configurations. The pulse width modulator isdriven at high speed by oscillator 944 which, in practice, operates at afrequency of about 40 kHz. This frequency of the oscillator driving thepulse width modulator and provides a series of current pulses at a highspeed switching rate to create an AC waveform at station WP. Thepolarity of the waveform is controlled by the logic or signal fromnetwork 950 having an input line 952 from waveform generator 960 and anoutput line 954 for controlling the polarity of the waveform outputtedfrom stage 912 of the Power Wave power source unit. The profile of thewaveform comprising a series of rapidly created pulses is controlled anddictated by waveform generator 960 having a select network 962 whichselects the desired waveform to be created at output terminals 912 a,912 b of stage 912. By the selected waveform from network 962, thedesired waveform is created for use by the electric arc weldingmechanisms 720 and 770. In accordance with the invention, the waveformbetween electrodes E1, E2 is adjusted as shown in system 900. Thewaveform of the trailing electrode, illustrated as electrode E3, iscontrolled by the circuits illustrated and discussed with respect toFIGS. 1-16. To control the waveform used for the series connectedelectrodes E1, E2, system 900 includes waveform adjusting circuits972-978, each having adjusting networks 972 a-978 a. Circuit 972 adjuststhe frequency of the waveform. After the waveform is selected by network962, a signal from circuit 972 adjusts the frequency of the AC waveform.In a like manner, the duty cycle of the waveform is controlled bycircuit 974. Duty cycle is the relative time the waveform is in thepositive polarity compared to the time in the negative polarity.Circuits 976 and 978 control the magnitude of the current during thenegative portion of the waveform or the positive portion of thewaveform. Circuit 976 is to adjust the magnitude of the negative portionof the waveform. Circuit 978 adjusts the magnitude of the positiveportion of the waveform. The waveform used for electrodes E1, E2 is anAC wave form. However, a DC waveform could be used for a trailingelectrode E3, although AC current is preferred in some embodiments.Indeed, for some embodiments it is preferred to use an AC waveform forall electrodes of electric arc welder 700. Other circuits have been usedto adjust the signal on line 970 to modulate and change the profile ofthe wave shape selected by network 962 to optimize welding at theintersection of electrodes E1, E2.

To increase the amount of current available for the welder shown in FIG.17 using the system shown in FIG. 19, a modified electric arc welder 980is shown in FIG. 20. Only the leading series connected electrodes E1, E2are illustrated; however, trailing electrodes E3 would be employed inwelder 980. The welder is used to obtain more welding current by formingmain power source 722 into a modified power source 722 a including twoseparate Power Wave units 982, 984. These units are connected inparallel to double the current capacity. Output leads 982 a, 982 b areconnected to terminals 724, 726, respectively. Output leads 984 a, 984 bare also connected to terminals 724, 726, respectively. Thus, welder 980operates as welder 700 shown in FIGS. 17 and 18 by using system 900shown in FIG. 19. By using parallel power sources, the available currentis increased, without increasing the capacity of the individual powersource. Furthermore, modules 982, 984 generate their own wire feedercontrol signals in lines 982 c, 984 c, respectively. Thus, wire feeders760, 762 are controlled by separately adjustable signals available ineach of the two power sources 982 and 984. Thus, the individual wirefeed speed of electrodes E1, E2 are adjusted using welder 980. A similarmodification of the preferred embodiment illustrated in FIGS. 17-19 isschematically illustrated in FIG. 21 which shows tandem electrode welder990 including a main power source 992 and a second power source 994. Themain power source 992 has output terminals 996 a and 996 b. Theseterminals are connected to leads 992 a and 992 b, respectively. Lead 992a connects the one output of power source 992 to contact 750 ofelectrode E1. Line 992 b is connected to line 1000 for current flow in apath to and from contact E2. To connect terminal 996 b in the path ofthe workpiece ground, second power source 994 is connected in seriesbetween terminal 996 b and workpiece W. Power source 994 has terminals998 a, 998 b. In this manner, second power source 994 is in series withthe lead 994 b connected to terminal 998 b. In this architecture,electrode E1 carries full current and the current to and from electrodeE1 is divided between electrode E2 and lead 994 b. This is like thearchitecture of FIG. 16. However, lead 994 a from terminal 998 a isconnected to lead 992 b from power source 992. Consequently, the twopower sources 992 and 994 are connected in series between the ground 994b and lead 992 a. Between the two power sources, lead 1000 is connectedto contact 752 of electrode E2. Consequently, electrodes E1 and E2 arein series with a ground current path through Power Wave power source994. By using this arrangement, the waveforms used for both power source992 and 994 are the same and are each created by a system 900 as shownin FIG. 19. Adjustments are made to the waveform process by power source994 to control the current flowing in the ground path of the weldershown in FIG. 21. Since two separate power sources are employed, wirefeeder 760 is controlled by the signal on line 992 c from power source992. A second wire feeder signal in line 994 c is controlled by powersource 994. As discussed with respect to the welder shown in FIG. 20,welder 990 has the advantage of being able to control wire feeders 760,762 separately without complex software in the power source digitalcontrol section. In essence, FIG. 20 shows a main power source with twoparallel modules. In FIG. 21 series connected modules are used; however,the second module is connected in series with the ground line to bettercontrol the current waveform in the ground return circuit or path.

The various technology concepts in FIGS. 1-16 can be applied to thewelder shown in FIGS. 16-21 and the various concepts in these lattermentioned welders can be incorporated into each other to accomplish theobjective of a tandem arc welder wherein the front two electrodes areconnected in series and having a current return path through theworkpiece.

FIG. 22 depicts a further exemplary embodiment of the present invention.Specifically, a welding system 1200 is shown for modified series arcwelding. The welding system 1200 contains at least three power supplies1210, 1220 and 1230 which are capable of welding for a submerged arcwelding process. The power supplies can be of the type describedpreviously. In another exemplary embodiment of the present invention,the power supplies can be of a type similar to the Power Wave AC/DC 1000SD, manufactured by The Lincoln Electric Company of Cleveland Ohio. Ofcourse, other types of power supplies can be utilized. Each of the powersupplies have positive output terminals 1211, 1221, and 1231(respectively), and negative output terminals 1215, 1225 and 1235(respectively), which are used to output the positive and negativeportions of the welding signal to the workpiece W, via positive andnegative leads. In embodiments of the present invention, the connectionof the leads is different than that done in the past. This is describedmore fully below, and this connection and control profile can provideimprovements over other series arc and modified series arc weldingsystems.

As described previously, for example with respect to FIG. 17, threeelectrodes E1, E2, and E3 can be used in embodiments of the invention.It is noted that aspects of the present invention are not limited to theuse of having only three electrodes. For example, additional electrodes(coupled to additional power supplies) can follow the trailing electrodeE3. Furthermore, in other exemplary embodiments of the presentinvention, it is not necessary to have the trailing electrode E3 (andpower supply 1230), which is typically used to provide additional fillermaterial into the weld.

In exemplary embodiments of the present invention, the positive leads1212/1222 of both the first and second power supplies 1210/1220 areelectrically connected to the leading contact 750, such that each of thefirst and second power supplies 1212/1222 deliver their respectivewelding signals to the same contact, and in the embodiment shown—theleading contact 750. In the embodiment shown in FIG. 22, the positivelead 1232 for the third power supply 1230 couples the power supply 1230to the trailing contact 786. The negative lead 1214 of the first powersupply 1210 is coupled to the workpiece W. Such a connection type isknown and can be accomplished via a ground clamp, etc. Similarly, thenegative lead 1234 is also coupled to the workpiece W via a groundclamp, etc. In the exemplary embodiment shown the negative leads1214/1234 from both the first and third power supplies 1210/1230 areconnected at a common bus point 1240, and the bus point 1240 is coupledto the workpiece W at a ground point 1250. Such a configuration can beutilized when the power supplies are located remotely from the workpieceW such that it is difficult to easily connect the respective leads 1214and 1234 to the workpiece. The bus point 1240 can be made of anyconductive type material or configuration, and for example can be simplya copper bar or plate. It is also noted that it is not necessary for theleads 1214 and 1234 to be grounded at the same point 1250, however sucha configuration may be advantageous depending on the configuration andsetup of the welding process.

It should be noted that although the power supplies 1210/1220/1230 areshown as separated components in FIG. 22, embodiments of the presentinvention are not limited in this regard. Specifically, embodiment ofthe present invention can have multiple power supply circuits integratedinto a single unit or housing. It is not required that each power supplydescribed herein be a entirely separate, individual power supply.

The negative lead 1224 of the second power supply 1220 is coupled to thesecond contact 752. The second power supply 1220 does not have a groundor negative lead which is directly connected to the workpiece W. This iscontrary to known systems. In such a configuration, at least some of thewelding current from the first and second power supplies 1210/1220passes from the lead contact 750 into the second contact 752 and backinto the second power supply 1220. It should be understood that duringwelding electrical current passes between the electrode E1 and theworkpiece W and between the electrode E1 and E2. That is, there are twocurrent returns paths—through the workpiece and ground point 1250 andthrough the negative lead 1224. Because of this, although a common arcis created with the electrodes E1 and E2, this common arc is effectivelymade up by an arc between the electrode E1 and the workpiece and theelectrode E1 and the electrode E2. Thus, there is no physical or realelectrical connection between the terminal 1225 on the second powersupply 1220 and the workpiece W.

As explained previously, the first and second electrodes E1 and E2 sharea common welding arc. As such, during welding at least some of thewelding current passes from the first electrode E1 to the secondelectrode E2 and back into the second power supply 1220 via the negativelead 1224.

In such a configuration, issues related to the impedance of the overallsystem are mitigated, if not eliminated all together. In prior systems,the ground path for the electrical current can significantly affect theresponsiveness of the welding system. That is, the overall impedance ofthe system is significantly affected by the ground path because theground path is a variable which can be difficult to control. Forexample, as the welding operation proceeds the distance between the arcand the ground point 1250 can change. This change in distance changesthe resistance of the circuit (between the arcs and the ground point1250) and as such the impedance of the overall electrical circuit wasunpredictable and would change during the welding operation. Moreover,the initial setup of the ground connection 1250 was also critical, asthe ground point 1250 location must have been carefully selected toprovide optimal system performance. However, again, even if the groundpoint 1250 was carefully selected as the welding process was ongoing thedistance to the ground point 1250 would change, thus again changing theimpedance of the system. It is known that the impedance of theelectrical system can greatly affect the overall responsiveness of thewelding power supplies, because the current flow is significantlyaffected by the impedance of the electrical circuit. In these priorsystems, the instability caused problems with the creation of the backbead (that is the bead created at the bottom of the workpiece W with thefirst root pass 802). This is because the common arc between electrodesE1 and E2 was unstable, as the current control from the power supplieswas adversely affected by the impedance changes. Furthermore, theinstability of the electrical circuits also adversely affected the arcstability of the trailing electrode E3. This instability would lead topoor weld quality and poor weld bead shape.

By having the negative lead 1224 of the second power supply 1220 onlyconnected to the contact 752 and not to the workpiece W, the abovediscussed impedance issues are mitigated. This allows the second powersupply 1220 to be able to be more responsive in controlling its currentoutput and thus provide a more stable welding arc and welding system.

To aid in understanding the above discussed embodiment, the operation ofan exemplary embodiment will now be discussed. In the embodiment shownin FIG. 22, the lead power supply 1210 is the master power supply, whilethe second power supply 1220 is the slave power supply, which receivesits operational commands from the master power supply 1210. Master/slaveoperational setups are well known in the welding industry and will notbe discussed in detail herein.

For operation a “total current” and “ground current” setting iscommunicated to and/or set on the master power supply 1210. The totalcurrent is the total amount of current (RMS current) delivered by boththe master 1210 and slave 1220 power supplies through their respectivepositive leads 1212/1222 to the contact 750. The ground current is theamount of the total current that is to be delivered to the workpieceW—that is, travel through the ground path. The difference between thetotal and the ground current is then delivered to the slave power supply1220 through the negative lead 1224. Because of such a current path theslave power supply 1220 can precisely control its current and as suchprecisely control the total current and the ground current. The slavepower supply's operation is not adversely affected by changing impedanceduring welding, or imprecisely initially determined impedance.

Because the ground current is the current going into the workpiece W itis the ground current which is determining the overall heat input intothe weld. As such, the heat input into the weld can be preciselycontrolled and optimized for a given welding operation. Thisoptimization can be accomplished by adjusting the relationship and/ordifference between the total current and the ground current. That is,the ground current can be reduced while the total current is maintained.Thus, the total deposition rate of the welding process can be unaffected(because the total current is maintained), while the total heat input isreduced (with the reduction of the amount of ground current beingsupplied to the weld). Alternatively, the deposition rate of the weldingprocess can be increased without increasing the overall heat input intothe weld. The total current utilized will dictate the overall depositionrate that can be achieved. Typically, the higher the total current thehigher the deposition rate. However, in prior systems the increase intotal current also meant an increase in heat input—which can bedisadvantageous, especially when welding thin workpieces W. Embodimentsof the present invention allow for a welding process to have anincreased deposition rate with no change in overall heat input. Forexample, an embodiment having a total current of 1,200 amps with aground current of 700 amps will have a higher deposition rate than aprocess having a total current of 1,000 amps and a ground current of 700amps, while the heat input into the workpiece W remains practically thesame in both applications.

In exemplary embodiments of the present invention, the current levels(in RMS current) of the first 1210 and second 1220 power supplies arenot the same. Specifically, in exemplary embodiments of the presentinvention, the lead power supply 1210 provides a higher RMS current tothe welding operation than the second power supply 1220. Stateddifferently, in embodiments of the present invention, the ground currentwill always be greater than 50% of the total current supplied. Forexample, if a total of 1,000 amps is desired for a welding operation andthe desired ground current is to be 600 amps, the leading power supply1210 will provide a total of 600 amps, while the second power supply1220 will provide the remaining 400 amps. In such a configuration theleading power supply 1210 will be the master power supply while thesecond power supply 1220 will be the slave power supply. As such, basedon the user settings (discussed further below), the master power supply1210 sets itself to provide the ground current, and instructs the slavepower supply 1220 to provide the remaining difference between thedesired total current and the ground current. (400 amps in the exampleabove.)

In exemplary embodiments of the present invention, the difference incurrent supplied by the master and slave power supplies 1210/1220 is inthe range of 50 to 600 amps. In further exemplary embodiments of thepresent invention, the different in current supplied is in the range of100 to 500 amps. By having a larger differential it is possible to use aslave power supply that will not have the same power rating as themaster power supply. This may help in reducing operational costs as asmaller power supply can be utilized for the slave power supply.

During operation, an operator would set both the desired total currentand desired ground current, and control circuitry within the mastersupply 1210 would cause both the master and slave power supplies1210/1220 to be set to their respective settings. In this configuration,each of the master and slave power supplies 1210/1220 are individuallyresponsible for delivering their respective currents to the weld. Insuch a configuration, the overall control of the total and groundcurrent is optimized. Thus, the current in the series arc is no longerdictated by the varying impedance in the circuit (for example, becauseof the presence of the workpiece) but rather is directly controlled bythe slave power supply 1220.

In embodiments of the present invention, the welding signals provided bythe master and slave power supplies are constant voltage signals. Infurther exemplary embodiments, the signals are constant current signals.Ideally, the power supplies 1210 and 1220 can be capable of providingboth types of welding signals based on the weld parameters.

FIG. 23 is a pictorial representation of an exemplary embodiment of awelding carriage assembly 1260 that can be utilized with embodiments ofthe systems described herein. The assembly 1260 contains a support 1261which secures each of the contacts 750, 752 and 786 relative to eachother during the welding operation. In the embodiment shown the contact786 is oriented normal to the welding surface and provides a stick outlength Y for the electrode E3. The stick out length Y can be any lengthwhich provides a suitable welding operation, and can be in the range of0.75 to 2.5 inches. The series contacts 750 and 752 are positionedadjacent to each other and are angled with respect to each other. Theangle 13 between the centerline of the contacts 750 and 752 can be inthe range of 15 to 45 degrees, and in some exemplary embodiments can bein the range of 25 to 35 degrees. Further, in the embodiment shown thecontact 752 is angled with respect to trailing contact 786 by the angleα. In exemplary embodiments of the present invention, the angle α is inthe range of 0 to 15 degrees. Each of the contacts 750 and 752 areoriented and positioned such that their respective electrodes E1 and E2intersect at a distance of approximately 0.25 inches above the bottomsurface of the workpiece W during welding. In other exemplaryembodiments, such as when welding thinner workpieces, the intersectionpoint is above the upper surface of the workpiece. The intersection ofthe electrodes should be chosen to optimize the welding operation, basedon at least the thicknesses of the workpiece(s) being welded. Further,each of the contacts 750 and 752 provide stick out distances W and Z,respectively, which are in the range of 0.75 to 2.5 inches. In exemplaryembodiments of the present invention the stick out distances W and Z arethe same, but in other embodiments the stick out distances can bedifferent.

Further, in the exemplary embodiment shown in FIG. 23 the contact 752and the trailing contact 786 are positioned on the support 1261 suchthat a distance X is measured between the respective electrodes E2 andE3. The distance X is selected so that the deposition from the electrodeE3 can be suitably deposited onto the weld created by the electrodes E1and E2. If X is too large, the deposition of the electrode E3 couldinterfere with slag created by the welding with E1 and E2. The slag iscreated by the use of flux, which is known by those in the industry.However, if the distance X is too small, then the respective weldingarcs could interfere with other, or cause too much overall heat inputinto weld zone. In exemplary embodiments of the present invention thedistance X is in the range of 3 to 6 inches. In other exemplaryembodiments the distance x is in the range of 4 to 5 inches.

The electrodes E1, E2 and E3 are to be selected based on desired weldingperformance (e.g., deposition rates, etc.) and weld characteristics(e.g., strength, etc.). As such, in some embodiments of the invention,the diameters of the electrodes E1, E2 and E3 can be different. Forexample, E1 can have a 3/16 inch diameter, while E2 has a ⅛ inchdiameter and E3 has a 5/32 inch diameter. Of course, other diameters canbe selected based on desired performance. Similarly, the composition ofthe electrodes can be different based on desired weld chemistry. Forexample, E1 and E2 can have the same chemistry, while E3 has a differentchemistry. Embodiments of the present invention are not limited in thisregard, as various chemistry combinations can be employed as desired.

Further, during operation the wire feed speeds for each of therespective electrodes E1, E2 and E3 do not have to be the same. Thus,during welding it is contemplated that the electrodes E1, E2 and E3 arefed into the weld at differing wire feed speeds, as desired for theneeded relative deposition rates. In the embodiment shown in FIG. 22,each of the separate wire feeders for the electrodes E1, E2, and E3 arecoupled to the power sources through the respective wire feed signalposts 1213, 1223, and 1233. In such an embodiment, each of the powersupplies control the operation of the wire feeders, and as such the wirefeed speeds can be different for each wire E1, E2 and E3. However, inanother exemplary embodiment of the present invention, the wire feedersfor each of the series wires E1 and E2 can be coupled to the post 1213of the master power supply 1210 such that they each receive the samesignal. In such an embodiment, the wire feed speeds for the series wiresE1 and E2 would be the same as each wire feeder is receiving the samecontrol signal. An example of such a configuration can be seen in FIG.17 where the lead 764 is coupled to both wire feeders 760 and 762.

FIG. 24 shows another exemplary embodiment of the present invention.Specifically, a welding system 1300 is shown which is similar inconstruction to that shown in FIG. 22. (Accordingly, like referencenumbers are not repeated for figure clarity.) A user interface 1310 isprovided having an input for total current 1311 and ground current 1312.The user interface 1310 is coupled to at least the master power supply1210 via connection 1313 to communicate the settings to the power supply1210 for welding. Although the user interface 1310 is shown as aseparate component in FIG. 24, embodiments of the present invention arenot limited to this configuration. Specifically, the user interface 1310with inputs 1311 and 1312 can be made integral to a power supply, forexample the master power supply 1210. Embodiments of the presentinvention are not limited in this regard. The user interface 1310 can beany known or type of system or device which allows for the input of userset points or data, such as a PC based device, etc. Embodiments of thepresent invention are not limited in this regard.

During operation, the master power supply 1210 receives the input totaland ground current settings and then sets its output current setting tomatch the ground current setting. The master power supply 1210 iscoupled to the slave power supply 1220 such that the slave power supply1220 sets its own current output to the difference between the totalcurrent and the ground current. Thus the combined output of the masterand slave power supplies 1210 and 1220 will be the desired totalcurrent. The master power supply 1210 can either communicate the desiredset point to the slave power supply (that is, the difference between thetotal and ground currents) or can simply communicate the total andground current settings so that the slave power supply will determineits own set point.

Of course, other configurations can be utilized. For example, the userinterface 1310 can be coupled to both the master and slave powersupplies 1210/1220 and communicate the setting information to each sothat they may set the appropriate operational set points for the powersupplies. Either the set points can be communicated to the master andslave power supplies or each of the respective power supplies 1210/1220can determine and set their own respective set points. The userinterface 1310 can also be only coupled to the slave power supply 1220which then communicates the set point(s) to the master supply 1210,which then controls aspects of the welding operation.

In the exemplary embodiment shown in FIG. 24 a link 1319 exists betweenthe master power supply 1210 and the third power supply 1230. This linkallows the powers supplies to communicate with each for operationalpurposes. That is, the master power supply 1210 can communicate at leastone operational parameter to the third power supply 1230. For example,in an embodiment of the present invention, the master power supply 1210is communicating a phase angle setting to the trailing power supply1230, which can be a user input setting to aid in stabilizing thewelding arcs. For example, if the welding waveforms for the series andtrailing arcs are balanced then the waveforms can be in-phase. However,if either or both of the waveforms are unbalanced, then the trailing arcwaveform should be set out-of-phase with the series arc waveform. Thewaveforms can be out of phase by 1 to 359 degrees and should be set toprovide a stable welding arc.

Further, as shown in FIG. 24, embodiments of the present invention canhave either voltage or current sense leads (or both) 1317/1321 connectedto the workpiece W. The use of voltage/current sense leads is generallyknown and need not be discussed in detail herein. Sense leads aretypically used as feedback leads to allow the respective power supplies1210/1230 monitor and control their operation. In the embodiment shown,the slave power supply 1220 does not have a sense lead connected to theworkpiece W. In fact, the slave power supply 1220 has no directconnection with the workpiece W.

As described above, embodiments of this aspect of the invention providestable modified series arc welding because the control over the currentand the arc generated by the master and slave power supplies is moreprecise. Therefore, embodiments of the present invention can providemuch better control and better quality over a wide range of workpiecethicknesses, without any adverse affects from excessive heat input. Thatis, embodiments of the present invention can weld workpieces havingthicknesses in the range of ¼ to 1 inch thick (for example), and withthe adjustment of the ground current setting the varying thicknesses canbe easily accommodated. For example, when welding thinner materials theground current (the current going into the workpiece) can be reduced,while the total current remains unchanged. In such a situation theoverall heat input into the thinner material is reduced but a desireddeposition rate is maintained. Therefore, the settings for the groundcurrent and the total current can be based on at least the thickness ofthe workpiece to be welded and a user can set each of these settingstaking into account the thickness. For thinner workpieces a user caninput a total current which allows for fast welding speeds but a groundcurrent which will prevent too much heat input into the workpiece, whichis problematic with thinner workpieces. This is advantageous over knownsystems which require less current (and accordingly heat input) whenwelding thinner materials. Because of these advantages, high strengthsteels (such as those used in the shipbuilding industries) can be weldedfrom a single side, having a high quality back bead structure and withmuch better control. This means that embodiments of the presentinvention can provide significant travel speed improvements over knownmethods. Embodiments of the present invention can achieve travel speedsin the range of 25 to 35 inches/min, even in the thinner and thickerworkpieces, which traditionally require slower travel speeds. In anotherexemplary embodiment travel speeds can range between 15 and 40inches/min. Of course, it is contemplated that higher and lower travelspeeds may be achieved.

In further exemplary embodiments of the present invention, variouswelding waveform parameters can be adjusted to optimize weld performancebased on the workpiece thickness, and other properties and based on thedesired weld parameters. Specifically, wave balance, wave offset,frequency and phase angle of the welding waveforms can be optimized toachieve desired welding properties and performance. In exemplaryembodiments of the present invention, and as previously discussed, asquare wave profile can be utilized, as opposed to a sine wave profile.It is known that square wave profiles can provide increased efficiencybecause the current and voltage of the welding waveform spends more timeat the peak values. The use of square wave profiles can provideincreased arc stability, the ability to weld thicker pieces with asingle welding pass, and the ability to weld thinner plates at fasterspeeds and reduced overall heat input.

Wave balance refers to the DC+ component of a welding waveform. That is,a wave having a 25% balance is a wave having 25% of its cycle positivewhile the remaining 75% is negative. This is graphically represented inFIG. 25, in which both a negative balanced and balanced wave is shown.Similarly, FIG. 26 shows a positive unbalanced wave as compared to abalanced wave. In exemplary embodiments of the present invention, it isdesirable to use a neutral or negatively balanced wave for the serieselectrode E1 and E2—that is a wave balance of 50% or less. The use of anegative balance increases the melt off of the welding electrodes (E1,E2 and E3). The wave balance of the welding waveforms can be tailored toachieve increased deposition while also decreasing penetration. Inexemplary embodiments of the present invention, the trailing electrodeE3 can have a wave balance that is positively balanced, that is greaterthan 50%.

Wave offset refers to a plus or minus shift of the current waveform withrespect to the 0 current crossing. Thus, offset shifts the amplitude ofthe current to be either more positive or more negative, as opposed tobalance which affects the amount of time that a current is eitherpositive or negative. Offset can be used to control the amount ofpenetration into the workpiece W during welding. Furthermore, offsetcontrol can be utilized to improve arc stability when welding near thelower limit of the current range for a specific electrode diameter. FIG.27 graphically depicts a square wave having no offset and a square wavehaving a negative offset. As can be seen, the negative offset waveformhas been shifted such that the currents peaks have been shifted to bemore negative (and less positive). Embodiments of the present inventioncan have offsets which are in the range of +/−25% of the peak amperage(positive or negative).

In exemplary embodiments of the present invention the waveform frequencycan also be employed to provide optimal welding parameters. For example,by increasing the frequency of the waveforms the welding bead width isreduced and the convexity of the weld bead is increased. Further, bydecreasing the waveform frequency more weld time is available at thepeak current and voltage values, while less overall time is spent in thetransition regions of the waveform. As such, welding can become moreefficient. In exemplary embodiments of the present invention, thefrequency of the welding waveforms can be between 20 and 100 Hz.

Phase angle is the angular separation of multiple AC current paths. FIG.28 shows two current paths having a 90 degree phase angle difference. Itis known that the electrical phase angle between two independent ACarcs, working in tandem, affects the stability of the arcs and the weldpool. Thus, phase angle can affect arc stability, bead shape,penetration and bead edge appearance. The phase angle can be set at anyangle between 0 and 360 degrees, depending on the desired weld beadperformance and characteristics.

In exemplary embodiments of the present invention where more penetrationis desired, but reduced filler metal is needed (for example in butt weldtype joints) the wave balance is greater than 50% and a positive offsetcan be utilized. In embodiments requiring more of a balance betweenpenetration and filler metal deposition a balance of 50% or less can beutilized. In other embodiments requiring little penetration, butsignificant fill (for example, V-notch grooves) the balance should beless than 50%, using a high frequency—in the range of 20 to 100 Hz, andnegative offset values. In some embodiments it may be possible to usefrequencies below 20 Hz or higher than 100 Hz, but stability of thewelding operation will need to be maintained.

In exemplary embodiments of the present invention, it may be beneficialto tune the welding waveform of the trailing electrode E3 to have morepenetration than that of the series electrodes E1 and E2. This isbecause it may be desirable to have the trailing electrode E3 penetratefurther into the bead made by electrodes E1 and E2 for bead shapeproperties.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these embodiments. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the following claims.

What is claimed is:
 1. A welding system, comprising: a first weldingpower supply having a first positive output terminal and a firstnegative output terminal, where said first positive output terminal iscoupled to a first contact tip and said first negative output terminalis coupled to a workpiece; and a second welding power supply having asecond positive output terminal and a second negative output terminal,where said second positive output terminal is coupled to said firstcontact tip and said second negative output terminal is coupled to asecond contact tip; wherein said second negative output terminal is notcoupled to said workpiece, and wherein each of said first and secondcontact tips are oriented to direct a first welding electrode and asecond welding electrode, respectively, to a common welding arc forwelding said workpiece.
 2. The welding system of claim 1, furthercomprising at least a third power supply having a third positive outputterminal and a third negative output terminal, where said third positiveoutput terminal is coupled to a third contact tip and a said thirdnegative terminal is coupled to said workpiece.
 3. The welding system ofclaim 1, wherein said first power supply supplies a first weldingcurrent having a first RMS value to said first welding electrode andsaid second power supply provides a second welding current to said firstwelding electrode, where said first RMS current is higher than saidsecond RMS current.
 4. The welding power supply of claim 3, wherein saidfirst RMS current is higher than said second RMS current by 50 to 600amps.
 5. The welding power supply of claim 1, wherein said first andsecond power supplies provide a total RMS current to said common weldingarc and an RMS current provided by said first power supply is greaterthan 50% of said total RMS current.
 6. The welding power supply of claim1, wherein at least one of said first and second power supplies iscoupled to a user interface having at least a total current and groundcurrent input capability for user inputs.
 7. The welding power supply ofclaim 1, further comprising a welding carriage assembly containing eachof said first and second contact tips and securing each of said firstand second contact tips in a fixed position for welding such that eachof said first and second electrodes can intersect.
 8. The welding powersupply of claim 7, wherein said welding carriage assembly also containsa third contact tip coupled to a third power supply, where said thirdcontact tip is oriented to direct a third welding electrode to saidworkpiece during welding and wherein said third contact tip ispositioned behind, in a travel direction, of said second contact tipsuch that a distance between said second welding electrode and saidthird welding electrode is in the range of 3 to 6 inches.
 9. The weldingsystem of claim 1, further comprising a first wire feeder for providingsaid first welding electrode and a second wire feeder for providing saidsecond welding electrode, wherein each of said first power supplycontrols both of said first and second wire feeders.
 10. The weldingsystem of claim 2, wherein said first power supply is coupled to saidthird power supply to control an operational parameter of said thirdpower supply.
 11. The welding system of claim 3, wherein a magnitude ofat least one of said first and second RMS currents and a sum of saidfirst and second RMS currents is based on at least a thickness of saidworkpiece.
 12. A method of welding, comprising: coupling a firstpositive output of a first power supply to a first contact tip and afirst negative output of said first power supply to a workpiece to bewelded; coupling a second positive output of a second power supply tosaid first contact tip and a second negative output of said second powersupply to a second contact tip such that said second negative output isnot coupled to said workpiece during welding; directing a first weldingelectrode to said workpiece through said first contact tip; directing asecond welding electrode to said workpiece through said second contacttip such that said first and second electrodes share a common weldingarc; providing a first RMS current from said first power supply to saidfirst welding electrode; providing a second RMS current from said secondpower supply to said first welding electrode.
 13. The method of claim12, wherein said first RMS current is larger than said second RMScurrent.
 14. The method of claim 12, wherein said first RMS current islarger than said second RMS current by 50 to 600 amps.
 15. The method ofclaim 12, further comprising entering into a user interface a totalcurrent setting and a ground current setting, where said total currentsetting determines the sum of said first and second RMS currents, andthe second RMS current is a difference between the total current settingand the ground current setting.
 16. The method of claim 12, furthercomprising directing a third welding electrode to said workpiece, wheresaid third electrode is coupled to a third power supply and where saidthird electrode is positioned 3 to 6 inches behind said secondelectrode, in a travel direction, during welding.
 17. The method ofclaim 12, wherein a travel speed of said welding is in the range of 15to 40 inches per minute.
 18. The method of claim 12, wherein a wire feedspeed of said first welding electrode is the same as a wire feed speedrate of said second welding electrode.
 19. The method of claim 12,wherein said first power supply communicates to said second power supplyan operational set point for said second RMS current.
 20. The method ofclaim 12, wherein said first welding electrode has a different diameterthan said second welding electrode.
 21. The method of claim 12, furthercomprising determining a magnitude of at least one of said first andsecond RMS currents and a total current setting, which is a sum of saidfirst and second RMS currents based on at least a thickness of saidworkpiece.